The present invention relates to a method for controlling multiple amplifier pump sources in a power sharing configuration in order to pump active gain media such as Erbium doped fiber amplifier modules and Ytterbium or Neodymium dual cladding fiber lasers.
Fiber optic technology has evolved significantly since the invention of the laser. Semiconductor lasers, fiber, and devices have been continuously improved in support of increasingly sophisticated fiber communication systems. The development of both high powered pump lasers at 1480 nm and 980 nm and rare earth doped fiber stimulated the realization of in-fiber amplifiers. Optical fiber amplifiers employing Erbium doped fiber as the gain medium allow communication signals to be power boosted prior to transmission or detection as well as to periodically compensate for transmission loss in a long repeatered communication system. These amplifiers have had a significant impact on the development of all-optical communication systems.
Development of components for fiber amplifiers has continued at a high rate by many suppliers who recognize the huge market for these products as the fiber communication industry continues to build systems which take advantage of the fiber amplifier. As an example of the accelerated development of components for fiber amplifiers, in the past few years pump laser manufacturers have worked to realize higher pump power levels, sought to build-in and measure reliability, and to add in-package isolators. Meanwhile, prices for components for fiber amplifiers have come down significantly. All of which indicates that the amplifier market is maturing and that there is a growing, large competitive base of commercial component vendors that are continuing to develop and supply fiber amplifiers.
The design of fiber optic communication systems has also evolved quickly with the advent of the erbium doped fiber amplifier. Amplifiers quickly supplanted regeneration repeaters as the gain medium of choice in communication systems. Long haul systems now use amplifiers to boost signals to compensate for fiber loss, rather than utilizing the previous method of detecting and regenerating the communication signals. Likewise, the electronic terminal equipment which initiates and terminates the optical signals on the fiber communication system has been modified to accommodate both high power optical booster amplifiers and low noise, low signal preamplifiers.
With the increasing demand for data communications capacity brought on by the demand for World Wide Web access and Internet services, optical communication systems are being driven to ever higher data capacity. The first large multi-wavelength undersea systems are now being realized.
These multi-wavelength systems require more sophisticated and costly terminal equipment to handle the greater volume of channels. Likewise, optical amplifier design has grown ever more complicated in response to increasing constraints from terminal equipment architects. Reliability of the amplifier has become a key challenge. In some instances, a terminal amplifier carries the entire flow of traffic. Meanwhile, unlike line optical amplifiers that are utilized in repeaters, where typical input and output power levels are relatively constant and predictable, which allows for less sophisticated amplifier designs, terminal amplifiers must handle a relatively larger range of input power levels and may have to deliver a user selectable output power level. In addition, unlike line amplifiers where bandwidth shaping integral to the amplifier is not required, in the terminal amplifier the output must be internally shaped to provide some measure of output power flatness. Thus, the gain requirements have become a second key challenge in terminal amplifier design.
It is known how to pump an Erbium doped fiber amplifier by utilizing a variety of configurations of one or more pump lasers. Generally, the gain medium is either co-pumped, counter-pumped or simultaneously co- and counter-pumped with either a 980 nm or 1480 nm semiconductor pump laser. A variable gain amplifier may be created by controlling the optical power of one or more of the pumps that feed the gain medium. A stabilized constant output amplifier can be constructed by controlling the pump power by utilizing a feedback loop that includes a signal detector on the amplifier output. Generally, the pumps and control circuitry are co-located with the amplifier optical circuit.
However, a drawback with the known methods of pumping an Erbium doped fiber amplifier by utilizing one or more pump lasers is the lack of the ability to share, combine or remove in real time, i.e., during amplifier operation, one or more of the pump sources without significantly or dramatically influencing the operation of the amplifier. Therefore, it would be desirable to provide for a reliable, redundantly pumped amplifier or laser configuration that permits real-time power sharing among the available pump sources.